A 3D analysis of yeast ER structure reveals how ER domains are organized by membrane curvature

TLDR

The peripheral ER in wild‑type yeast consists of cytoplasmic cisternae, numerous tubules, and a large plasma‑membrane–associated domain of tubules and fenestrated cisternae. The study aimed to map the three‑dimensional organization of yeast ER during six sequential stages of budding using electron tomography. Electron tomography was performed on yeast cells at each budding stage to generate a nanometer‑resolution 3‑D portrait of ER inheritance. The authors mapped ER domain distribution, size, and ribosome density across budding stages, revealing that loss of reticulons or Yop1 removes membrane curvature, alters ribosome density, and expands the plasma.

Abstract

We analyzed the structure of yeast endoplasmic reticulum (ER) during six sequential stages of budding by electron tomography to reveal a three-dimensional portrait of ER organization during inheritance at a nanometer resolution. We have determined the distribution, dimensions, and ribosome densities of structurally distinct but continuous ER domains during multiple stages of budding with and without the tubule-shaping proteins, reticulons (Rtns) and Yop1. In wild-type cells, the peripheral ER contains cytoplasmic cisternae, many tubules, and a large plasma membrane (PM)–associated ER domain that consists of both tubules and fenestrated cisternae. In the absence of Rtn/Yop1, all three domains lose membrane curvature, ER ribosome density changes, and the amount of PM-associated ER increases dramatically. Deletion of Rtns/Yop1 does not, however, prevent bloated ER tubules from being pulled from the mother cisterna into the bud and strongly suggests that Rtns/Yop1 stabilize/maintain rather than generate membrane curvature at all peripheral ER domains in yeast.